Weight Distribution and Sway Control -Obsolete for a Self Propelled Trailers?

[turbopilot]

Nothing to do with sway or J2807, but everything to do with the Rivian's pneumatic suspension system.

For those reading this interchange, it is exactly debates like this that need AI as a tie breaker. I have studied this subject as well as I can without getting an SAE membership. I have tried to confirm my facts with several sources. It appears Google Gemini is calling it right about this 5,000 lb WDH requirement found with many pickup truck tow vehicles.

The bottom line is this. For the Rivian they must use a high profile, high center of gravity, slab sided 11,000 lb trailer with 1,100 lbs on the tongue to run the test. In this configuration once it fails either the lateral g force requirement or the sway requirement without WDH, they can then continue the test up to the required maximum weight of 11,000 lbs using a WDH. Apparently most manufacturers that fail the test between 5,000 and 11,000 lbs without a WDH don't report the failure point in the test, instead they decide to slap on the WDH Required limitation at 5,000 lbs which is the default and call it a day.

If anyone else has better information please chime in. I visited this subject in detail several years ago and had an actual copy of the SAE J2807 test protocol but I can't find it right now.

So the 5,000 lb WDH required is sort of a "safe harbor" for a very demanding test involving an 11,000 lb trailer for trucks down to the half ton category. The mischief in structuring this test like this is that many trucks are "forced" to use these archaic, leveraged WDH systems that may be able to operate safely without them.

AI says much better than I can so here is how this SAE J2807 certification is arrived at.

From Google AI:

The question to Gemini:

Does this mean that if the truck can only pass the test with WDH at 11,000lbs it must require a WDH at 5,000lbs.

Gemini Response:

Not exactly. It’s better to think of the 5,000-lb limit as a pre-certified safety floor rather than a consequence of the 11,000-lb test.

Here is the nuance of how those two numbers interact:

1. The "Default" Safety Limit (5,000 lbs)​

In the world of light-duty trucks (half-tons and SUVs), 5,000 lbs is the industry-standard threshold for "weight-carrying" (standard ball hitch) towing.

• The Assumption: Engineers generally assume that up to 5,000 lbs, a typical vehicle's chassis, wheelbase, and suspension can handle the leverage of a trailer safely without mechanical assistance.
• The Testing: Rivian (and others) will test the vehicle without a WDH at this 5,000-lb mark. If it passes all the SAE J2807 handling and sway metrics, they can stamp it with a "5,000-lb Weight Carrying" rating.

2. The "Equipped" Rating (11,000 lbs)​

Once you go above that 5,000-lb floor, the physics change exponentially. The R1T might pass at 5,000 lbs, but it might fail the "Understeer" or "Sway Damping" test at 5,500 lbs.

• The Fork in the Road: Instead of capping the truck at 5,000 lbs forever, Rivian re-runs the tests with a Weight Distribution Hitch.
• The Result: The WDH "fixes" the physics failures that occurred at 5,500 lbs, allowing the engineers to keep piling on weight until they hit the next failure point—which for the R1T is 11,000 lbs.

3. Does the High End Force the Low End?​

No. If Rivian could theoretically pass the SAE J2807 sway and understeer tests at 8,000 lbs without a WDH, they would likely advertise an 8,000-lb "weight-carrying" limit.

However, they don't. This tells us that at some point shortly after 5,000 lbs, the R1T’s performance (likely the steering authority due to front-axle unloading) dropped below the SAE's strict safety requirements.

Why specifically 5,000 lbs?​

It is a "Class III" hitch standard. Most receiver hardware is designed such that:

• Below 5,000 lbs: The downward force (tongue weight) is manageable by the receiver and vehicle frame.
• Above 5,000 lbs: The rotational torque on the hitch receiver becomes high enough that a WDH is needed to "twist" that force back into the vehicle's frame more evenly.

In summary: The 5,000-lb requirement exists because that is the maximum weight at which Rivian can guarantee the truck meets SAE safety standards using just a standard ball. To go even one pound over that, you are moving into a "profile" where the truck only legally meets safety standards when the WDH is doing its job of restoring that front axle load.

 

[Kevin D Pem]

Sway has nothing to do with it. You're still confused. Rivian says no to towing anything over 5k without a WDH, end of story. Take it up with Rivian.

That applies to receivers as well. Plainly displayed in the literature and displayed on the tag. Tow capacity with and without a WDH.

it is the responsibility of the operator to use the proper equipment nessisary to safely tow the weights he/she plan to tow.

In case of accident, failure to do so shifts responsibility to that party. Produce all the claims you want,no matter how it was presented to you! If the injured party produces a manual in court for any manufacurered reciver hitch. And you didn't follow their guidelines! Well!

 

[Holdmybeer]

https://docs.google.com/document/u/...HuN8qK7GJrR_1mBz1Ohsk/mobilebasic?hl=en&pli=1

 

[Porterhouse]

When a manufacturer says you need a WD hitch for any tongue load over 500 lbs., he is saying that because he doesn't know what else you are carrying in the bed. If the bed is empty, you can safely carry more than 500 lbs. on the hitch ball. You do have to comply with the axle ratings stamped on the door placard, though.

Note that the purpose of a WD hitch is to prevent overloading the rear axle by putting some of the hitch load onto the front axle, thereby allowing the manufacturer to claim a higher towing rating.

Note also that a WD hitch is not a safety device (even though they are often sold as such). A WD hitch will diminish a tow vehicle's handling capability, meaning that you will not be able to go around a turn as fast if you use a WD hitch. Instead of being able to pull 0.5 Gs in a turn, you might only be able to pull 0.3 Gs. If you have to swerve to avoid an accident, you are more prone to jackknifing your rig. I recommend that you avoid these hitches and instead get a heavier, more robust tow vehicle to solve your weight problem.

 

[turbopilot]

I recommend that you avoid these hitches and instead get a heavier, more robust tow vehicle to solve your weight problem.

This is a point made often in these discussions, "Just get a bigger truck" to muscle your way out these boxes we are put in with the manufacturer recommendations about weight limits and WDH use.

I am towing an 8,200 lb trailer with a 2025 F-150 PowerBoost Platinum Model. The PowerBoost is the heaviest and most powerful F-150 made. It is an F-250 with a restricted payload.. My PowerBoost has a curb weight of 6,163 lbs and GVWR of 7,400 lbs. The lightest 2025 F-150 has a curb weight of 4,391 lbs with GVWR of 6,010 lbs. So my PowerBoost is 1,400 lbs heavier than the lightest F-150.

A 2025 F-250 Crew Cab gas truck (the next step up) has a curb weight of 6,041 lbs and a GVWR of 10,000 lbs. So before payload my F-150 PowerBoost is actually heavier than an F-250. But for towing my F-150 PowerBoost is grouped with all the lighter F-150 variants and requires an Weight Distribution Hitch. The lighter F-250 does not require a weight distribution hitch when towing a trailer heavier than 5,000 lbs.

Some will say but you can can have a 10,000 lb GVWR if you move to an F-250. But I don't need a 10,000 lb GVWR. For my missions I can tow the LightShip with a 7,400 lb GVWR with the PowerBoost. The additional 2,600 lb payload advantage with an F-250 is not important to me. The additional weight in the chassis to carry that additional load is not needed.

So when people say you can forget about a WDH by moving to an F-250 it makes no sense. I have an F-250 from a weight carrying perspective up to 7,400 lb GVWR.

This silly WDH requirement for my PowerBoost is just a way for Ford to lump a recommendation and keep it simple by saying all F-150's need a WDH ,most likely because the lightest F-150 failed the SAE J2807 test.

My F-150 PowerBoost is an F-250 by all the metrics except its ability to carry an additional 2,600 lbs of payload which I don't require.

If an F-250 gas model can pull a 8,200 lb LightShip without a WDH, there is no reason an F-150 hybrid cannot do the same thing since it is a heavier truck up to the 7,400 GVWR limit.

 

[TheLooks]

Then take it up with Ford. AI does not make something ok with the law.
I read all the pages here and this is my take on AI. It can only spit out what it takes in and cannot discern what is right and what is wrong. As I said in the other post about AI, I have been able to back it into a corner when it repeatedly told me I was wrong. It butters you up by praising how much you know about xyz......but you have to push it in a direction to get to the truth. OR your truth.

 

[Holdmybeer]

AI in it’s current iteration is only a tool, if you run your router clockwise around the outside edge of your workpiece it’s not the router’s fault it looks like you trimmed it with a hatchet.

 

[turbopilot]

Then take it up with Ford. AI does not make something ok with the law.
I read all the pages here and this is my take on AI. It can only spit out what it takes in and cannot discern what is right and what is wrong. As I said in the other post about AI, I have been able to back it into a corner when it repeatedly told me I was wrong. It butters you up by praising how much you know about xyz......but you have to push it in a direction to get to the truth. OR your truth.

I am glad you read the material but a condescending lecture is not helpful. A thoughtful analysis is much more constructive. Every criticism you attribute to AI is found on this forum with human input. Your response is an excellent example.

 

[turbopilot]

AI in it’s current iteration is only a tool, if you run your router clockwise around the outside edge of your workpiece it’s not the router’s fault it looks like you trimmed it with a hatchet.

Word salad dribble. You must have better things to do than type this kind of nonsense on a public forum. This stupid response resulted in everyone who is subscribed to the thread to get an email notification only to see some contorted analogy that adds nothing to the dialog.

 

[Kevin D Pem]

When I finally admitted I was wrong! I learned the truth! Not one minute before. No one could show me, I had to realize that Truth for myself.

 

[Holdmybeer]

When I finally admitted I was wrong! I learned the truth! Not one minute before. No one could show me, I had to realize that Truth for myself.

It’s called the “Dunning-kreuger Effect”. Cognitive bias where people with limited. competence in a field overestimate their own ability. Some get past it , apparently some never will.

 

[Kevin D Pem]

It’s called the “Dunning-kreuger Effect”. Cognitive bias where people with limited. competence in a field overestimate their own ability. Some get past it , apparently some never will.

I was,as usual, using a parable type comment. Why current AI can't produce 100% accurate results.

On the same curve, why some people can't see the obvious.

AI will never exceed the abilities of it's Creator. Just say'in. If it produces output that you find impressive! Well!

 

[TheLooks]

I am glad you read the material but a condescending lecture is not helpful. A thoughtful analysis is much more constructive. Every criticism you attribute to AI is found on this forum with human input. Your response is an excellent example.

Nothing condescending in it. I find your posts very condescending to everyone else! You and your AI know more then everyone.....because you say so! I really don't have a dog in this fight, but I have been reading about your Lightship since you posted about it originally. Almost from the get go you attacked anyone who questioned anything about it. But to also attack everyone's post as internet drivel that should be filtered out by superior thinking is beyond arrogant.
So, good luck with your high priced Rube Goldberg device, the answer to a question almost no one is asking. And the future will determine if you have a DeLorean or a desirable first edition of a new wave in camping/Rving.

 

[Holdmybeer]

I was,as usual, using a parable type comment. Why current AI can't produce 100% accurate results.

On the same curve, why some people can't see the obvious.

AI will never exceed the abilities of it's Creator. Just say'in. If it produces output that you find impressive! Well!

However we can't let perfect be the enemy of the good. Last year every AI enabled robot running a parallel course in the Beijing E-Town half marathon dnf. This year an autonomous AI enabled robot set the world record by 7 minutes.
AGI or SuperIntelligence will exceed the abilities of its creator, that is arguably the problem.

 

[turbopilot]

I think it is important to update this thread dealing with the subject of WDH’s and the LightShip. Nothing creates more emotion on RV forums than the subject of weight distribution hitches. So many "experts", with so little detailed analysis. Everything about this subject is governed by a one size fits all SAE J2807 protocol for testing tow vehicle performance followed by most US manufacturers. Most US manufacturers have used this protocol since 2015. It is behind most of the towing constraint recommendations you see published by tow vehicle manufacturers.

But SAE J2807 aside, the need for a WDH must be considered in the light of each tow vehicle and towable RV. Every combination is unique, with so many variables. It is one thing for the tow vehicle to “pass” the protocol and an entirely different matter whether it specifically applies to your tow vehicle and towable RV combination. The SAE J7804, as applied by most manufacturers, only “passes” a tow vehicle if it is towing the heaviest trailer certified for the tow vehicle and it must be a high profile, high center of gravity trailer. It may or may not apply to your specific tow vehicle and trailer configuration.

The issues of sway control, the relationship of lateral G acceleration to front end stability and the choice of a tow vehicle are very important to any serious person considering a towable RV. It is a complicated subject that many will say is easily solved by getting a bigger truck. That solution is aways on the table. But it gets complicated because bigger trucks may not have many features and attributes desired by those who only tow occasionally. The biggest issue is that big trucks are "BIG" and not conducive to being a daily driver, as well as serving the role of an occasional tow vehicle. And they may lack important features. Many “BIG” trucks won’t even fit in a standard household garage.

Why all this fuss? The F-150 Powerboost, with a 7.2 kW generator, is the only tow vehicle available today that can pull a LightShip without the necessity of the LightShip ever visiting an EV charging station. But a well optioned PowerBoost is right at the edge of the envelope to tow an 8,400 GVWR LightShip. The more options on the PowerBoost the closer you are to the edge of the envelope. Currently no bigger truck is available with an integral, built in generator.

The reality is that there MAY be no way to tow a LightShip, with a fully optioned PowerBoost, without using a mechanical leverage (WDH) because of the mathematical realities of one section in the SAE J2807 towing standard that deals with lateral stability. This issue may be inescapable with a Powerboost towing a LightShip. Specifically, the standard mandates that a tow vehicle and trailer must be able to withstand a 0.3g lateral acceleration maneuver (like an emergency lane change) without entering a divergent sway or losing steering authority. You cannot pass that standard without a correct amount traction on the front tires. This constraint can be aided by returning weight to the front axle. The question is how much weight is enough given the trailer in tow. The physics are compelling. For my PowerBoost, the physics suggests I need to add weight to the front axle on my Powerboost once the hitch weight exceeds 660 lbs. I currently have 850 lbs on the hitch with the Lightship fully provisioned ready to camp.

Because of the LightShip attributes of a very low center of gravity and extraordinary aerodynamic characteristics, the PowerBoost/LightShip combination should easily pass the sway requirements of the SAE J2807 test, without a WDH, but the 0.3g lateral acceleration test may fail without a moving more weight to the front axle.

The SAE J2807 was not designed to cover your use case, it was worked out to provide a level of safety for the worst case the tow vehicle may encounter. For the F-150 PowerBoost it means it must pass the SAE J2807 test, without a WDH, pulling an 11,000lb, high center of gravity, high frontal area, slab sided trailer.

Accepting that I have upgraded the tires on the PowerBoost and added a rear sway control bar to provide an extra level of protection against lateral “g” steering issues and will continue to use the awful Curt 17062 Round Bar WDH approved by LightShip. This will provide lateral g protection until I can determine if my configuration will pass the .3 g lateral acceleration maneuver without a WDH.

I think it is possible that the PowerBoost towing a Lightship can pass the .3g lateral acceleration test of the SAE J2807 standard with the right tires, at the right inflation pressure and the addition of a rear sway bar. But I need to find a calibrated 300’ circle with a painted line, on perfectly flat ground, with the right pavement, to run my own test. These calibrated circles can only be found at a few automotive proving grounds in the US.

While the numbers change based on tow vehicle, everything in this analysis applies to any other EV, HEV, EREV or ICE tow vehicle. The constraints become less and less for bigger and heavier tow vehicles, but the physics are the same. Most EV tow vehicles have the same recommendations about the use of WDH devices.

I am going to continue to evaluate ways to pass the lateral g acceleration constraint by exploring options other than using mechanical leverage to return weight to the front axles. However, right now a comprehensive mathematical analysis suggests it may be hard to do. While it does work, these mechanical leverage devices are a PITA to put on and take off every time you unhitch from the trailer. And they are very heavy. More on that later.